Orthodontics is the branch of dentistry that deals with the prevention or correction of irregularities of the teeth and jaws. These irregularities may affect the oral health, as well as possibly the physical, aesthetic and/or mental wellbeing of affected individuals.
Tooth positioning and orofacial bone structures can currently be altered using manual, mechanical systems, generally consisting of a combination of, for example, wires, brackets, bands, chains, springs and elastics, a system commonly referred to as “dental braces” or simply “braces”. Braces are commonly used to generate, transmit and maintain forces, force vectors and moments to individual teeth or between teeth, activating various biomechanical processes within the affected tissues to facilitate tooth movement.
It is generally accepted that a force of zero magnitude will not induce any tooth movement, whereas a force of excessive magnitude might damage cells surrounding the tooth and may also cause root resorption and excessive patient discomfort. This gives rise to the concept that an optimal force exists, between a zero force and a force of excessive magnitude, which would be capable of inducing the maximum rate of tooth movement without causing any tissue damage, root resorption, as little as possible patient discomfort, and a minimum level of additional, adverse side-effects.
Conventional orthodontic systems have a number of shortcomings with regard to this optimal orthodontic force. Firstly, the majority of orthodontic systems rely purely on mechanical components, which are relatively inflexible once put in place. The placement of the mechanical components by the practitioner largely determines the forces exerted on the teeth and virtually no controlled changes can be made thereto without manually changing the configuration of the mechanical components. Furthermore, many of the components used, which as stated above include, amongst others, springs, wires and elastic bands, do not accurately generate a constant desired force over a longer period of time or over a specified distance, largely due to the physical characteristics of these components. This makes it improbable that the forces transmitted to the teeth are representative of the optimal force for any continuous period of time. The result of other than optimal forces being applied to the orofacial structures can induce the problems mentioned above.
The problems mentioned above may, however, not be the biggest concern regarding the treatment of, for example, malocclusion and other abnormalities of the orofacial structures. Equally important is the need to accurately determine the optimal force that would result in the most effective treatment, as this optimal force may differ from patient to patient. To the applicant's knowledge, it has not yet been possible to quantitatively describe such an optimal force. Numerous attempts have been made to describe a universally applicable relationship between force magnitude and the resultant rate of tooth movement, but current scientific wisdom seems to suggest that these relationships are much more appropriately determined on an individual basis or even on a tooth-specific basis for a given patient.
Based on the data from a number of studies of which the applicant is aware, it was concluded that the reviewed experimental results were negatively affected by, amongst others, the inability to accurately calculate stresses in the periodontal ligament of a given tooth, the inability to control the type of tooth movement, the different phases of tooth movement during an applied force and large inter-individual variations or even variations within individuals. As a result, no exact ideal force magnitude could be recommended.
It has also been found that large individual variations exist for the mean rate of tooth movement achieved under application of the same forces. A possible explanation that has been proposed for this phenomenon is that each individual could have his or her own optimal force that would produce the maximum rate of tooth movement.
More recently, the view has been adopted that the movement of teeth is a result of externally applied mechanical stimuli and the subsequent biological reactions that take place within the periodontium. Inherent to the mechanical stimuli are various parameters including the force magnitude, direction, point of application, frequency of application and duration of application. Still further parameters could play an important role when non-static forces are considered such as the force profile, oscillatory frequency and oscillatory amplitude. The above parameters in combination with the anatomical and physiological properties inherent to the affected tooth/teeth lead to yet further factors affecting tooth movement. A certain mechanical stimulus applied to a specific case will lead to cellular strains, shear stresses and pressure changes within the affected tissues. Each of these could further affect the resulting tooth movement thereby emphasizing the importance of the externally applied stimulus.
The effect of unidirectional micro currents on the rate of tooth movement has also been studied by the application of a low-frequency pulsating force. It was found that the rate of movement for the tooth to which a pulsing force was applied was greater than that of a control tooth in the same individual.
It is clear that the force magnitude is not the only factor affecting the rate of tooth movement and that various other factors exist that need to be taken into consideration and controlled to induce the maximum rate of tooth movement. The optimal orthodontic force can then be described as the force that, to the best of scientific knowledge, is most effective in producing a desired outcome of a certain orthodontic treatment. This may be the force that, if applied to one or multiple teeth, would result in the maximum rate of tooth movement, while at the same time avoiding any adverse short or long term tissue damage, minimising patient discomfort or aiding in achieving any other desired outcomes. The force can be in any direction or around any axis in a three dimensional space and can vary in magnitude, direction, frequency, profile or point of application. The optimal orthodontic force can be patient specific, as well as age or health specific, and can further differ for each tooth, group of teeth, type of tooth movement or other type of treatment.
In the remainder of this specification the term “optimal orthodontic force” should be interpreted to be such an optimal force when applied in an orthodontic environment. The term “optimal force” should in turn be interpreted to have a corresponding meaning but capable of being applied in any reconstructive or corrective surgery where relative bone or tissue movement is achieved by means of the application of a mechanical force or moment over a period of time. In addition, the terms “force” and “stimulus” are used interchangeably and should be interpreted broadly to include any combination of forces and moments or either individually.